This invention relates to architecture for correlation of signals in one of a plurality of channels with simultaneous decorrelation with respect to signals in other channels.
In radar systems using array antennas, the signals from each separate antenna (or from subgroups of the antennas of the array) are processed by down converting to produce a baseband signal having amplitude and phase. The amplitude and phase of the signal received by each antenna may be represented by a complex number such as A+j.PHI.. In general, the amplitude of the signals received by each antenna of an antenna array will be equal, so long as the antenna is distant from the target. However, the relative phase of the signal received by each antenna will differ markedly from those of other antennas in the array, depending upon the direction from which the signal arrives. In general, the phase of the received signals will not be the same for all antennas of the array even if the target is on the boresight, because of the lateral dimensions of the array. Modern radar systems using array antennas use phase shifters or delay elements associated with each antenna and possibly with subgroups of antennas to create phase shifts which allow the preferred direction of reception (main beam) to be moved about within the volume of interest. In modern phased-array antennas, the signals from the antennas are summed, possibly with phase shifts, to receive signals from predetermined portions of the volume being examined in preference to signals from other directions. Sophisticated array antenna systems can be subdivided so as to produce several main antenna beams or preferred directions of reception so as to simultaneously track several targets. Whether there be one main beam or several, the antenna nevertheless may respond at a low level to signals received from directions other than the main beam direction.
In the context of wartime use of a radar system, the desired signal being tracked by the main beam may be obscured by one or more extraneous signals being received from non-preferred directions, because the extraneous signals have a very high power level. This might be the result of efforts to jam the radar system. The effect of reception from undesired directions can be reduced by sidelobe cancelling circuits which include networks, such as the modified Gram-Schmidt N-channel decorrelation networks described in the article "An Efficient Algorithm and Systolic Architecture for Multiple Channel Adaptive Filtering" by Yuen et al., published in the IEEE Transactions on Antenna and Propagation., Vol. 36, No. 5, May 1988. In the arrangement described therein, signals received over multiple channels, one of which represents the desired signal, are correlated in the desired channel and decorrelated from the signals received from the other channels. If all the channels are receiving the undesired signal, the desired signal in the first channel can be rendered substantially free of the undesired signals. The modified Gram-Schmidt arrangement uses a plurality of dual-input, single-output decorrelation processors (DP) arranged in ranks, with the outputs of some of the processors being broadcast (i.e. connected to the inputs of multiple other processors) to inputs of all of the DPs of the next rank. In addition, the interconnections are asymmetrically arranged. The broadcasting requirement of the modified Gram-Schmidt arrangement imposes limitations in a hardware layout, and the asymmetry makes the hardware implementation difficult. In addition to use for reducing the effects of jamming, N-channel decorrelation arrangements find other uses in radar systems, such as decorrelating the speed-representative signals at the outputs of a Doppler processor. A more symmetrical organization for multiple-channel adaptive filtering or decorrelation is desired.